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Abstract:

A solder degradation information generation apparatus related to a motor
drive circuit that includes a power supply, a converter, a smoothing
capacitor, and an electric motor is disclosed. The solder degradation
information generation apparatus includes a semiconductor element that
forms an upper arm of the converter and is bonded to a substrate via a
solder, the substrate being cooled by a coolant, a measuring unit
configured to measure a temperature of the semiconductor element and a
processing device that generates information indicating a degradation
state of the solder based on a measurement result of the measuring unit
that is obtained during a period in which the smoothing capacitor is
charged.

Claims:

1. A solder degradation information generation apparatus related to a
motor drive circuit that includes a power supply, a converter, a
smoothing capacitor, and an electric motor, the solder degradation
information generation apparatus comprising: a semiconductor element that
forms an upper arm of the converter and is bonded to a substrate via a
solder, the substrate being cooled by a coolant; a measuring unit
configured to measure a temperature of the semiconductor element; and a
processing device that generates information indicating a degradation
state of the solder based on a measurement result of the measuring unit
that is obtained during a period in which the smoothing capacitor is
charged.

2. The solder degradation information generation apparatus of claim 1,
wherein the processing device causes the smoothing capacitor to be
charged at a time of starting up a system related to the motor driver
circuit, and generates the information based on the measurement result of
the measuring unit obtained during the period in which the smoothing
capacitor is thus charged.

4. A solder degradation information generation apparatus related to a
motor drive circuit that includes a power supply, a filter capacitor, a
converter, a smoothing capacitor, and an electric motor, the solder
degradation information generation apparatus comprising: a first
switching element that forms an upper arm of the converter and is bonded
to a first substrate via a first solder, the first substrate being cooled
by a first coolant; a second switching element that forms a lower arm of
the converter and is bonded to a second substrate via a second solder,
the second solder being different from the first solder, the first
substrate being cooled by a second coolant; a first measuring unit
configured to measure a temperature of the first switching element; and a
processing device that turns on the first switching element and turns off
the second switching element to cause the smoothing capacitor to be
discharged, and generates information indicating a degradation state of
the first solder based on a measurement result of the first measuring
unit that is obtained during a period in which the smoothing capacitor is
thus discharged.

5. The solder degradation information generation apparatus of claim 4,
wherein the processing device, at a time of shutting down a system
related to the motor drive circuit, turns on the first switching element
and turns off the second switching element to cause the smoothing
capacitor to be discharged, and generates the information based on the
measurement result of the first measuring unit obtained during the period
in which the smoothing capacitor is thus discharged.

6. The solder degradation information generation apparatus of claim 4,
further comprising a second measuring unit configured to measure a
temperature of the second switching element, wherein the processing
device, after the smoothing capacitor has been discharged, turns on the
second switching element to cause the filter capacitor to be discharged,
and generates information indicating a degradation state of the second
solder based on the measurement result of the second measuring unit
obtained during the period in which the filter capacitor is thus
discharged.

7. A solder degradation information generation apparatus related to a
motor drive circuit that includes a power supply, a filter capacitor, a
converter, a smoothing capacitor, and an electric motor, the solder
degradation information generation apparatus comprising: a switching
element that forms a lower arm of the converter and is bonded to a
substrate via a solder, the substrate being cooled by a coolant, a
measuring unit configured to measure a temperature of the switching
element; and a processing device that turns on the switching element to
cause the filter capacitor to be discharged, and generates information
indicating a degradation state of the solder based on a measurement
result of the measuring unit that is obtained during a period in which
the filter capacitor is thus discharged.

8. The solder degradation information generation apparatus of claim 7,
wherein the processing device, at a time of starting up a system related
to the motor driver circuit, turns on the switching element to cause the
filter capacitor to be discharged and generates the information based on
the measurement result of the measuring unit obtained during the period
in which the filter capacitor is thus discharged.

9. A solder degradation information generation apparatus related to a
motor drive circuit that includes an inverter, a smoothing capacitor, and
an electric motor, the solder degradation information generation
apparatus comprising: a third switching element that forms an upper arm
of the inverter related to a first phase and is bonded to a third
substrate via a third solder, the third substrate being cooled by a third
coolant; a fourth switching element that forms an upper arm of the
inverter related to a second phase different from the first phase and is
bonded to a fourth substrate via a fourth solder different from the third
solder, the fourth substrate being cooled by a fourth coolant; a
measuring unit configured to measure a temperature of the third switching
element or the fourth switching element; and a processing device that
turns on the third switching element and the fourth switching element
simultaneously to cause the smoothing capacitor to be discharged, and
generates information indicating a degradation state of the third solder
or the fourth solder based on a measurement result of the measuring unit
that is obtained during a period in which the smoothing capacitor is thus
discharged.

10. The solder degradation information generation apparatus of claim 9,
wherein the processing device, at a time of shutting down a system
related to the motor driver circuit, turns on the third switching element
and the fourth switching element simultaneously to cause the smoothing
capacitor to be discharged and generates the information based on the
measurement result of the measuring unit obtained during the period in
which the filter capacitor is thus discharged.

Description:

FIELD

[0001] The present invention is related to a solder degradation
information generation apparatus.

BACKGROUND

[0002] Japanese Laid-open Patent Publication No. 2009-19953 (referred to
as "Patent Document 1", hereinafter) discloses a technique for detecting
a degradation of a solder bonding portion by simultaneously applying a
life measuring pulse of about 10 micro millimeter second to IGBTs
(Insulated Gate Bipolar Transistor) on upper and lower sides to cause a
short circuit current to be generated.

[0003] However, according to an configuration disclosed in Patent Document
1, a circuit formed when the IGBTs on upper and lower sides are turned on
simultaneously has a substantially low impedance, which may lead to a
problem in that a substantially large short circuit current is generated
instantaneously when the IGBTs on upper and lower sides are turned on
simultaneously.

[0004] Therefore, an object of the present invention is provide a solder
degradation information generation apparatus that can generate
information indicating a degradation state of a solder without generating
a short circuit current.

SUMMARY

[0005] According to the present invention, a solder degradation
information generation apparatus related to a motor drive circuit that
includes a power supply, a converter, a smoothing capacitor, and an
electric motor is provided, the solder degradation information generation
apparatus includes:

[0006] a semiconductor element that forms an upper arm of the converter
and is bonded to a substrate via a solder, the substrate being cooled by
a coolant;

[0007] a measuring unit configured to measure a temperature of the
semiconductor element; and

[0008] a processing device that generates information indicating a
degradation state of the solder based on a measurement result of the
measuring unit that is obtained during a period in which the smoothing
capacitor is charged.

BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a diagram illustrating an example a motor drive circuit
related to a solder degradation information generation apparatus
according to a first embodiment of the present invention.

[0010] FIG. 2 is a diagram illustrating an example of an installed state
of a free wheeling diode 11.

[0011] FIG. 3 is a diagram illustrating a configuration of an information
processing system related to the solder degradation information
generation apparatus according to a second embodiment.

[0012] FIG. 4 is an example of a flowchart of a solder degradation
determination process executed by a processing device 100.

[0013] FIG. 5 is a diagram schematically illustrating flow of a current at
a time of pre-charging.

[0015] FIG. 7 is another example of a flowchart of a solder degradation
determination process executed by a processing device 100.

[0016] FIG. 8 is a diagram schematically illustrating flow of a current at
a time of discharging a smoothing capacitor 20.

[0017] FIG. 9 is another example of a flowchart of a solder degradation
determination process executed by the processing device 100.

[0018] FIG. 10 is a diagram schematically illustrating flow of a current
at a time of discharging a filter capacitor 22.

[0019] FIG. 11 is a diagram illustrating a configuration of an information
processing system related, to the solder degradation information
generation apparatus according to the second embodiment.

[0020] FIG. 12 is an example of a flowchart of a solder degradation
determination process executed by a processing device 100A.

[0021] FIG. 13 is a diagram schematically illustrating flow of a current
at a time of discharging the smoothing capacitor 20.

DESCRIPTION OF EMBODIMENTS

[0022] In the following, embodiments will be described with reference to
the accompanying drawings.

[0023] FIG. 1 is a diagram illustrating an example a motor drive circuit 2
related to a solder degradation information generation apparatus
according to a first embodiment of the present invention. FIG. 2 is a
diagram illustrating an example of an installed state of a free wheeling
diode 11. It is noted that, in FIG. 2, referential numerals in brackets
indicate components related to a first switching element 10 and a second
switching element 12 other than the free wheeling diode 11.

[0024] The motor drive circuit 2 is used for a hybrid vehicle or an
electric vehicle.

[0025] The motor drive circuit 2 includes a direct-current power supply
VL, an inverter 3, a converter 4, a smoothing capacitor 20, a filter
capacitor 22 and an electric motor 5.

[0026] The first switching element 10 and the second switching element 12
form the converter 4 together with an inductor Id that is coupled to a
midpoint PO between the first switching element 10 and the second
switching element 12 to perform a stepping-up and stepping-down
operations. The inverter 3 is coupled to the electric motor 5.

[0027] The first switching element 10 is an IGBT (Insulated Gate Bipolar
Transistor) in this example. It is noted that the first switching element
10 may be another switching element, instead of IGBT, such as a MOSFET
(metal oxide semiconductor field-effect transistor), etc. The first
switching element 10 is coupled to the free wheeling diode 11 (an example
of a first semiconductor element) in parallel, as illustrated in FIG. 1.

[0028] The free wheeling diode 11 is installed on a first substrate 60 via
a solder 53, as illustrated in FIG. 2. The first substrate 60 is bonded
to a heat sink 70. The heat sink 70 includes a lower side (an opposite
side with respect to the first substrate 60) that contacts a first
coolant. A lower side surface of the heat sink 70 may include fins 70a
formed therein. It is noted that, in the example illustrated in FIG. 2,
the first substrate includes three layers in which aluminum plates are
provided on opposite sides of a ceramic substrate such as aluminum
nitride, etc. Alternatively, the first substrate 60 may include copper
plates on the opposite sides of the ceramic substrate, or may be formed
by a single copper plate (i.e., a heat spreader). In the case where the
first substrate 60 includes only the copper plate, the first substrate 60
is bonded to the heat sink 70 via an insulating layer such as an
insulation film, etc.

[0029] It is noted that, in FIG. 2, a pump 80 for supplying the first
coolant is schematically illustrated at a coolant channel formed on the
lower side of the heat sink 70. The heat sink 70 forms a flow (a
circulation) of the coolant through the fins. 70a of the heat sink 70 via
a supply channel 82. The first coolant is arbitrary, and may be air, or a
liquid such as a LLC (Long Life Coolant).

[0030] Although the illustration is omitted, the first switching element
10 is installed on the first substrate 60 via a first solder 51 (see FIG.
2), as is the case with the free wheeling diode 11. The first switching
element 10 and the free wheeling diode 11 may be formed by a single chip
as an RC-IGBT (Reverse Conducting-Insulated Gate Bipolar Transistor). In
this case, the RC-IGBT (another example of a first semiconductor element)
is bonded to the first substrate 60 via the solder 53.

[0031] Although the illustration is omitted, the second switching element
12 (an example of a second semiconductor element) is installed on a
second substrate 62 via a second solder 52 (see FIG. 2), as is the case
with the free wheeling diode 11. The second switching element 12 is an
IGBT, in this example. The second switching element 12 is coupled to a
free wheeling diode 13 in parallel, as illustrated in FIG. 1. The second
substrate 62 on which the second switching element 12 is installed is
different from the first substrate 60 on which the first switching
element 10 is installed and electrically insulated from the first
substrate 60. The second substrate 62 on which the second switching
element 12 is installed is cooled by a second coolant. The second coolant
may be the same as the first coolant (i.e., a coolant shared between the
upper and the lower arms) or may be different from the first coolant
(i.e., the second coolant flows through a coolant channel different from
the first coolant channel).

[0032] Although the illustration is omitted, the free wheeling diode 13 is
installed on the substrate, as is the case with the free wheeling diode
11. The substrate on which the free wheeling diode 13 is installed may be
the same as the second substrate 62 on which the second switching element
12 is installed. The second switching element 12 and the free wheeling
diode 13 may be formed by a single chip as the RC-IGBT.

[0033] The smoothing capacitor 20 is provided in parallel with respect to
the first switching element and the second switching element 12 between a
positive pole line 30 and a negative pole line 32.

[0034] The filter capacitor 22 is provided in parallel with respect to the
second switching element 12 between a positive pole and a negative pole
of the direct-current power supply VL. A main switch SW1 is provided
between the direct-current power supply VL and the filter capacitor 22.
The main switch SW1 includes a relay. The main switch SW1 may include a
limitation resistor R1 and a pre-charge relay RL1 in parallel. It is
noted that, in the example illustrated in FIG. 1, the main switches SW1
are provided on the opposite sides of the direct-current power supply VL;
however, one of the main switches SW1 may be omitted.

[0035] FIG. 3 is a diagram illustrating a configuration of an information
processing system related to the solder degradation information
generation apparatus.

[0036] The solder degradation information generation apparatus 1 includes
a processing device 100, a first temperature sensor 41, a second
temperature sensor 42, and a temperature sensor 43.

[0037] The processing device 100 includes a computer.

[0038] The first temperature sensor 41 (an example of a first measuring
unit) measures a temperature of the first switching element 10. The first
temperature sensor 41 may be incorporated in a chip that includes the
first switching element 10.

[0039] The second temperature sensor 42 (an example of a second measuring
unit) measures a temperature of the second switching element 12. The
second temperature sensor 42 may be incorporated in a chip that includes
the second switching element 12.

[0040] The temperature sensor 43 (an example of a measuring unit) measures
a temperature of the free wheeling diode 11. It is noted that, in the
case where the first switching element 10 and the free wheeling diode 11
are formed by a single chip as the RC-IGBT, the temperature sensor 43 may
measures the temperature of the first switching element 10. In this case,
the first temperature sensor 41 or the temperature sensor 43 can be
omitted.

[0041] The processing device 100 includes a control part 102, a storage
part 104, and a degradation determination part 106.

[0042] The control part 102 controls the converter 4 by applying pulses to
respective gates of the first switching element 10 and the second
switching element 12. Further, the control part 102 controls the main
switch SW1 (FIG. 1).

[0043] The storage part 104 stores measurement results of the first
temperature sensor 41, the second temperature sensor 42 and the
temperature sensor 43 (also simply referred to as "temperature sensors 41
through 43", hereinafter).

[0044] The degradation determination part 106 outputs information
indicating degradation states of the first solder 51, the second solder
52 and the solder 53 (also simply referred to as "solders", hereinafter)
based on change manners of the measured values of the temperature sensors
41 through 43. The information indicating the degradation states of the
solders directly or indirectly represent the degradation states of the
solders.

[0045] FIG. 4 is an example of a flowchart of a solder degradation
determination process executed by the processing device 100.

[0046] In step S400, the control part 102 turns on the main switch SW1.
When the main switch SW1 is turned on, the system related to the motor
drive circuit 2 is started up. When the main switch SW1 is turned on, the
current flows as an arrow I1 schematically illustrated in FIG. 5, which
increases a voltage (i.e., a potential difference between P1 and P2)
across the smoothing capacitor 20 (i.e., the smoothing capacitor 20 is
pre-charged). Accordingly, a loss is generated at the free wheeling diode
11, which increases the temperature of the free wheeling diode 11.

[0047] In step S402, the control part 102 determines whether the charging
(pre-charging) of the smoothing capacitor 20 is completed. The control
part 102 may determine that charging of the smoothing capacitor 20 is
completed after a lapse of a predetermined time from the timing of
starting the pre-charge. Alternatively, the control part 102 may
determine that charging of the smoothing capacitor 20 is completed when
the voltage across the smoothing capacitor 20 becomes greater than or
equal to a predetermined threshold. If it is determined that the charging
(pre-charging) of the smoothing capacitor 20 is completed, the process
routine goes to step S406, otherwise process routine goes to step S404.

[0048] In step S404, the control part 102 stores the measured value of the
temperature sensor 43 at that time in the storage part 104. When the
control part 102 completes the process of step S404, the control part 102
performs the processes from step S402 after a lapse of a predetermined
time again.

[0049] In step S406, the degradation determination part 106 generates,
based on the measurement result of the temperature sensor 43 (i.e., the
measurement result of the temperature sensor 43 during the charging of
the smoothing capacitor 20) stored in the storage part 104, the
information indicating the degradation state of the solder 53 immediately
below the free wheeling diode 11. For example, the degradation
determination part 106 determines the degradation state of the solder 53
based on the measurement result of the temperature sensor 43 during the
charging of the smoothing capacitor 20, and generates information
representing a determination result. For example, the degradation
determination part 106 determines whether an increased amount of the
measured value of the temperature sensor 43 (i.e., an increased amount of
the temperature of the free wheeling diode 11) during the charging of the
smoothing capacitor 20 is greater than or equal to a predetermined
threshold Tth. In this case, when the increased amount of the measured
value of the temperature sensor 43 during the charging of the smoothing
capacitor 20 is greater than or equal to the predetermined threshold Tth,
the degradation determination part 106 may determine that there is a
degradation, otherwise the degradation determination part 106 may
determine that there is no degradation. The degradation determination
part 106 may call attention to a user by turning on an alert indicator,
etc., when the degradation determination part 106 determines that there
is a degradation.

[0050] FIG. 6 is a diagram illustrating heating/radiating characteristic
curves that are obtained as the measurement result of the temperature
sensor 43 during the charging of the smoothing capacitor 20. In step
S406, the degradation determination part 106 may determine the
degradation state of the solder 53 based on the heating/radiating
characteristic curve to output the determination result.

[0051] In FIG. 6, a curve "A" indicates a case where there is no
degradation in the solder 53 (i.e., a conforming item), and a curve "B"
indicates a case where there is a degradation in the solder 53 (i.e., a
degraded item). As illustrated in FIG. 6, a peak temperature Tp in the
state in which the solder 53 is degraded becomes higher than that in the
state in which the solder 53 is not degraded. This is because
transmission of the heat to the first substrate 60 is limited by the
degradation of the solder 53. Thus, the degradation determination part
106 of the processing device 100 may determine the degradation state of
the solder 53 based on the peak temperature Tp obtained from the
heating/radiating characteristic curve.

[0052] It is noted that the determination result of the degradation state
of the solder 53 may be output in a binary manner (i.e., simply whether
there is a degradation or not) or may be output in three or more steps.
Further, the degradation determination part 106 of the processing device
100 may output a numeral itself between the peak temperatures Tp (i.e.,
the difference with respect to the confirming item) as the determination
result of the degradation state of the solder 53. Alternatively, the
degradation determination part 106 may output the heating/radiating
characteristic curve itself. It is noted that element on which the
information is output may be a display installed on the vehicle, a
terminal used at a dealer, an external server, etc. In this case, an
inspector of the dealer, for example, may determine the degradation state
of the solder 53 by checking such numeral or the heating/radiating
characteristic curve.

[0053] According to the process illustrated in FIG. 4, the degradation
determination part 106 can generate, based on the measurement result of
the temperature sensor 43 during the charging of the smoothing capacitor
20, the information indicating the degradation state of the solder 53
immediately below the free wheeling diode 11. Thus, the degradation
determination part 106 can generate the information indicating the
degradation state of the solder 53 by effectively utilizing an operation
(i.e, the pre-charge operation) at the time of stating up the system
related to the motor drive circuit 2. Thus, the degradation determination
part 106 can effectively generate the information indicating the
degradation state of the solder 53 by utilizing an ordinary operation of
the system related to the motor drive circuit 2. Further, the current
flowing through the free wheeling diode 11 during the charging of the
smoothing capacitor 20 does not take an instantaneous large value,
because there is the limitation resistor R1 in the circuit as illustrated
in FIG. 5 (i.e., because a low impedance is prevented). Therefore, a
probability of a failure of the free wheeling diode 11 due to the current
at the time of determining the degradation can be reduced. It is noted
that, even in a configuration in which there is no limitation resistor
R1, the current flowing through the free wheeling diode 11 during the
charging of the smoothing capacitor 20 does not take an instantaneous
large value, because there is the inductance Id in the circuit. Thus,
even in the configuration in which there is no limitation resistor R1,
the probability of the failure of the free wheeling diode 11 due to the
current at the time of determining the degradation can be reduced.

[0054] It is noted that, in the process illustrated in FIG. 4, the
degradation determination part 106 generates the information indicating
the degradation state of the solder 53 based on the measurement result of
the temperature sensor 43 obtained over a whole charge period of the
smoothing capacitor 20; however, this is not indispensable. For example,
the degradation determination part 106 may generate the information
indicating the degradation state of the solder 53 based on the
measurement result of the temperature sensor 43 obtained over a part of
the whole charge period of the smoothing capacitor 20 or at a
predetermined timing (the peak value of the temperature sensor 43, for
example) during the charge period.

[0055] FIG. 7 is another example of a flowchart of the solder degradation
determination process executed by the processing device 100.

[0056] In step S700, the control part 102 turns off the main switch SW1.
When the main switch SW1 is turned off, the system related to the motor
drive circuit 2 is stopped.

[0057] In step S701, the control part 102 turns on the first switching
element 10 and turns off the second switching element 12. As a result of
this, the current flows as schematically illustrated by an arrow 12 in
FIG. 8, which causes electric charges accumulated in the smoothing
capacitor 20 to move to the filter capacitor 22. In other words, a
voltage across the filter capacitor 22 increases (i.e., the smoothing
capacitor 20 is discharged). Accordingly, the loss is generated at the
first switching element 10, which increases the temperature of the first
switching element 10.

[0058] In step S702, the control part 102 determines whether the
discharging of the smoothing capacitor 20 is completed. The control part
102 may determine that discharging of the smoothing capacitor 20 is
completed after a lapse of a predetermined time from the timing of
starting the discharge. Alternatively, the control part 102 may determine
that discharging of the smoothing capacitor 20 is completed when the
voltage across the filter capacitor 22 becomes greater than or equal to a
predetermined threshold. Alternatively, the control part 102 may
determine that discharging of the smoothing capacitor 20 is completed
when the voltage across the smoothing capacitor 20 becomes less than or
equal to a predetermined threshold. If it is determined that the
discharging of the smoothing capacitor 20 is completed, the process
routine goes to step S706, otherwise process routine goes to step S704.
It is noted that, if it is determined that the discharging of the
smoothing capacitor 20 is completed, the control part 102 may turn off
the first switching element 10.

[0059] In step S704, the control part 102 stores the measured value of the
first temperature sensor 41 at that time in the storage part 104. When
the control part 102 completes the process of step S704, the control part
102 performs the processes from step S702 after a lapse of a
predetermined time again.

[0060] In step S706, the degradation determination part 106 generates,
based on the measurement result of the first temperature sensor (i.e.,
the measurement result of the first temperature sensor 41 during the
discharging of the smoothing capacitor 20) stored in the storage part
104, the information indicating the degradation state of the first solder
51 immediately below the first switching element 10. The process itself
may be the same as the process in step S406 described above except that
the measurement result of the first temperature sensor 41 is used and the
degradation state of the first solder 51 is determined.

[0061] According to the process illustrated in FIG. 7, the degradation
determination part 106 can generate, based on the measurement result of
the first temperature sensor 41 during the discharging of the smoothing
capacitor 20, the information indicating the degradation state of the
first solder 51 immediately below the first switching element 10. Thus,
the degradation determination part 106 can effectively generate the
information indicating the degradation state of the first solder 51 by
utilizing a discharge operation that is generally performed at the time
of stopping the system related to the motor drive circuit 2. Further, the
current flowing through the first switching element 10 during the
discharging of the smoothing capacitor 20 does not take an instantaneous
large value, because there is the inductance Id in the circuit as
illustrated in FIG. 8 (i.e., because a low impedance is prevented).
Therefore, a probability of a failure of the first switching element 10
due to the current at the time of determining the degradation can be
reduced.

[0062] It is noted that, in the process illustrated in FIG. 7, the
degradation determination part 106 generates the information indicating
the degradation state of the first solder 51 based on the measurement
result of the first temperature sensor 41 obtained over a whole discharge
period of the smoothing capacitor 20; however, this is not indispensable.
For example, the degradation determination part 106 may generate the
information indicating the degradation state of the first solder based on
the measurement result of the first temperature sensor 41 obtained over a
part of the whole discharge period of the smoothing capacitor 20 or at a
predetermined timing during the discharge period.

[0063] FIG. 9 is another example of a flowchart of the solder degradation
determination process executed by the processing device 100.

[0064] In step S900, the control part 102 turns off the main switch SW1.
When the main switch SW1 is turned off, the system related to the motor
drive circuit 2 is stopped.

[0065] In step S901, the control part 102 turns off the first switching
element 10 and turns on the second switching element 12. As a result of
this, the current flows as schematically illustrated by an arrow 13 in
FIG. 10, which causes electric charges accumulated in the filter
capacitor 22 to move to ground. In other words, the filter capacitor 22
is discharged. Accordingly, the loss is generated at the second switching
element 12, which increases the temperature of the second switching
element 12.

[0066] In step S902, the control part 102 determines whether the
discharging of the filter capacitor 22 is completed. The control part 102
may determine that discharging of the filter capacitor is completed after
a lapse of a predetermined time from the timing of starting the
discharge. Alternatively, the control part 102 may determine that
discharging of the filter capacitor 22 is completed when the voltage
across the filter capacitor 22 becomes less than or equal to a
predetermined threshold. If it is determined that the discharging of the
filter capacitor 22 is completed, the process routine goes to step S906,
otherwise process routine goes to step S904. It is noted that, if it is
determined that the discharging of the filter capacitor 22 is completed,
the control part 102 may turn off the second switching element 12.

[0067] In step S904, the control part 102 stores the measured value of the
second temperature sensor 42 at that time in the storage part 104. When
the control part 102 completes the process of step S904, the control part
102 performs the processes from step S902 after a lapse of a
predetermined time again.

[0068] In step S906, the degradation determination part 106, based on the
measurement result of the second temperature sensor 42 (i.e., the
measurement result of the second temperature sensor 42 during the
discharging of the filter capacitor 22) stored in the storage part 104,
the information indicating the degradation state of the second solder 52
immediately below the second switching element 12. The process itself may
be the same as the process in step S406 described above except for that
the measurement result of the second temperature sensor 42 is used and
the degradation state of the second solder 52 is determined.

[0069] According to the process illustrated in FIG. 9, the degradation
determination part 106 can generate, based on the measurement result of
the second temperature sensor 42 during the discharging of the filter
capacitor 22, the information indicating the degradation state of the
second solder 52 immediately below the second switching element 12. Thus,
the degradation determination part 106 can effectively generate the
information indicating the degradation state of the second solder 52 by
utilizing a discharge operation that is generally performed at the time
of stopping the system related to the motor drive circuit 2. Further, the
current through the second switching element 12 during the discharging of
the filter capacitor 22 does not take an instantaneous large value,
because there is the inductance Id in the circuit as illustrated in FIG.
10 (i.e., because a low impedance is prevented). Therefore, a probability
of a failure of the second switching element 12 due to the current at the
time of determining the degradation can be reduced.

[0070] It is noted that, in the process illustrated in FIG. 9, the
degradation determination part 106 generates the information indicating
the degradation state of the second solder 52 based on the measurement
result of the second temperature sensor 42 obtained over a whole
discharge period of the filter capacitor 22; however, this is not
indispensable. For example, the degradation determination part 106 may
generate the information indicating the degradation state of the second
solder 52 based on the measurement result of the second temperature
sensor 42 obtained over a part of the whole discharge period of the
filter capacitor 22 or at a predetermined timing during the discharge
period.

[0071] It is noted that the process illustrated in FIG. 9 may be performed
independently from the process illustrated in FIG. 7; however, it is
preferred that the process illustrated in FIG. 9 is performed after the
process illustrated in FIG. 7. In this case, for example, when the
determination result of step S702 illustrated in FIG. 7 becomes "YES",
the process from step S901 illustrated in FIG. 9 is started. According to
such a combination, the degradation determination part 106 can generate
the information indicating the degradation states of the first solder 51
and the second solder 52 by utilizing a series of operations that are
generally performed at the time of stopping the system related to the
motor drive circuit 2.

[0072] Next, with reference to FIG. 11, the solder degradation information
generation apparatus according to a second embodiment of the present
invention is described. The motor drive circuit to which the solder
degradation information generation apparatus according to the second
embodiment is applied may be the same as the motor drive circuit 2
illustrated in FIG. 1. However, the motor drive circuit to which the
solder degradation information generation apparatus according to the
second embodiment is applied may be a configuration in which the
converter 4 in the motor drive circuit 2 illustrated in FIG. 1 is
omitted.

[0073] The solder degradation information generation apparatus according
to the second embodiment differs from the solder degradation information
generation apparatus 1 according to the first embodiment mainly in that
the solder degradation information generation apparatus according to the
second embodiment generates information indicating a degradation state of
a solder immediately below a switching element related to the inverter 3.

[0074] Here, the switching element of a U-phase upper arm of the inverter
3 is referred to as "a third switching element 15", and the switching
element of a W-phase lower arm of the inverter 3 is referred to as "a
fourth switching element 16".

[0075] The third switching element 15 is installed on a third substrate
(not illustrated) via a third solder (not illustrated), as is the case
with the free wheeling diode 11 illustrated in FIG. 2. The third
substrate is cooled by a third coolant as is the case with first
substrate 60 illustrated in FIG. 2.

[0076] The fourth switching element 16 is installed on a fourth substrate
(not illustrated) via a fourth solder (not illustrated), as is the case
with the free wheeling diode 11 illustrated in FIG. 2. The fourth
substrate is different from the third substrate and electrically
insulated from the third substrate. The fourth substrate is cooled by a
fourth coolant as is the case with first substrate. 60 illustrated in
FIG. 2. The fourth coolant may be the same as the third coolant (i.e., a
shared coolant) or may be different from the third coolant (i.e., the
fourth coolant and the third coolant flow in separated channels).

[0077] FIG. 11 is a diagram illustrating a configuration of an information
processing system related to the solder degradation information
generation apparatus according to the second embodiment.

[0080] The third temperature sensor 44 (an example of a third measuring
unit) measures a temperature of the third switching element 15. The third
temperature sensor 44 may be incorporated in a chip that includes the
third switching element 15.

[0081] The fourth temperature sensor 45 (an example of a fourth measuring
unit) measures a temperature of the fourth switching element 16. The
fourth temperature sensor 45 may be incorporated in a chip that includes
the fourth switching element 16.

[0082] The processing device 100A includes a control part 102A, a storage
part 104A, and a degradation determination part 106A.

[0083] The control part 102A controls the inverter 3 by applying pulses to
respective gates of the respective switching elements (including the
third switching element 15 and the fourth switching element 16) of the
inverter 3. Further, the control part 102A controls the main switch SW1
(FIG. 1).

[0084] The storage part 104A stores the measurement results of the third
temperature sensor 44 and the fourth temperature sensor 45.

[0085] The degradation determination part 106A outputs information
indicating degradation states of the third solder and the fourth solder
based on change manners of the measured values of the third temperature
sensor 44 and the fourth temperature sensor 45. The information
indicating the degradation states of the third solder and the fourth
solder may be the same as described above in connection with the first
embodiment. A way of determining the degradations of the third solder and
the fourth solder may be the same as the way described above in
connection with the first embodiment.

[0086] FIG. 12 is an example of a flowchart of the solder degradation
determination process executed by the processing device 100A.

[0087] In step S1200, the control part 102A turns off the main switch SW1.
When the main switch SW1 is turned off, the system related to the motor
drive circuit 2 is stopped.

[0088] In step S1201, the control part 102A turns on the third switching
element 15 and turns on the fourth switching element 16. In other words,
the control part 102A turns on the third switching element 15 and the
fourth switching element 16 simultaneously. It is noted that, at that
time, the control part 102A turns off other switching elements of the
inverter 3, and turns off the first switching element 10 of the converter
4 if the converter 4 is provided. As a result of this, the current flows
as schematically illustrated by an arrow 14 in FIG. 13, which causes
electric charges accumulated in the smoothing capacitor 20 to move to
ground via the third switching element 15 and the fourth switching
element 16. In other words, the smoothing capacitor 20 is discharged.
Accordingly, the loss is generated at the third switching element 15 and
the fourth switching element 16, which increases the temperatures of the
third switching element 15 and the fourth switching element 16.

[0089] In step S1202, the control part 102A determines whether the
discharging of the smoothing capacitor 20 is completed. The control part
102A may determine that discharging of the smoothing capacitor 20 is
completed after a lapse of a predetermined time from the timing of
starting the discharge. Alternatively, the control part 102A may
determine that discharging of the smoothing capacitor 20 is completed
when the voltage across the smoothing capacitor 20 becomes less than or
equal to a predetermined threshold. If it is determined that the
discharging of the smoothing capacitor 20 is completed, the process
routine goes to step S1206, otherwise the process routine goes to step
S1204. It is noted that, if it is determined that the discharging of the
smoothing capacitor 20 is completed, the control part 102A may turn off
the third switching element 15 and the fourth switching element 16.

[0090] In step S1204, the control part 102A stores the measured values of
the third temperature sensor 44 and the fourth temperature sensor 45 at
that time in the storage part 104A. When the control part 102A completes
the process of step S1204, the control part 102A performs the processes
from step S1202 after a lapse of a predetermined time again.

[0091] In step S1206, the control part 102A generates, based on the
measurement results of the third temperature sensor 44 and the fourth
temperature sensor 45 (i.e., the measurement results of the third
temperature sensor 44 and the fourth temperature sensor 45 during the
discharging of the smoothing capacitor 20) stored in the storage part
104A, the information indicating the degradation states of the third
solder immediately below the third switching element 15 and the fourth
solder immediately below the fourth switching element 16. The process
itself may be the same as the process in step S406 described above except
that the measurement results of the third temperature sensor 44 and the
fourth temperature sensor 45 are used and the degradation states of the
third and fourth solders are determined.

[0092] According to the process illustrated in FIG. 12, the degradation
determination part 106A can generate, based on the measurement results of
the third temperature sensor 44 and the fourth temperature sensor 45
during the discharging of the smoothing capacitor 20, the information
indicating the degradation states of the third solder immediately below
the third switching element 15 and the fourth solder immediately below
the fourth switching element 16. Thus; the degradation determination part
106A can effectively generate the information indicating the degradation
states of the third and fourth solders by utilizing a discharge operation
that is generally performed at the time of stopping the system related to
the motor drive circuit 2. Further, the current through the third
switching element 15 and the fourth switching element 16 during the
discharging of the smoothing capacitor 20 does not take an instantaneous
large value, because there are inductances and resistors of the electric
motor 5 in the circuit as illustrated in FIG. 13 (i.e., because a low
impedance is prevented). Therefore, a probability of a failure of the
third switching element 15 and the fourth switching element 16 due to the
current at the time of determining the degradation can be reduced.

[0093] It is noted that, in the process illustrated in FIG. 12, the
degradation determination part 106A generates the information indicating
the degradation states of the third and fourth solders based on the
measurement results of the third temperature sensor 44 and the fourth
temperature sensor 45 obtained during the discharge period of the
smoothing capacitor 20; however, this is not indispensable. For example,
the degradation determination part 106A may generate the information
indicating only one of the degradation states of the third and fourth
solders based on the corresponding one of the measurement results of the
third temperature sensor 44 and the fourth temperature sensor 45 obtained
during the discharge period of the smoothing capacitor 20.

[0094] Further, according to the process illustrated in FIG. 12, as an
example, the third switching element 15 is related to the U-phase upper
arm of the inverter 3, and the fourth switching element 16 is related to
the W-phase lower arm of the inverter 3; however, this is not
indispensable. For example, the third switching element 15 may be related
to the U-phase upper arm of the inverter 3, and the fourth switching
element 16 may be related to the V-phase lower arm of the inverter 3.
Similarly, the third switching element 15 may be related to the V-phase
upper arm of the inverter 3, and the fourth switching element 16 may be
related to the W-phase or U-phase lower arm of the inverter 3. Similarly,
the third switching element 15 may be related to the W-phase upper arm of
the inverter 3, and the fourth switching element 16 may be related to the
V-phase or U-phase lower arm of the inverter 3. Further, the process
illustrated in FIG. 12 may be performed in sequence for each pair of the
switching elements according to these combinations. In this case, the
degradation determination part 106A may generate the information
indicating the degradation states of the solders related to the
respective pairs by dividing the whole discharge period of the smoothing
capacitor 20 into a plurality of time sections.

[0095] Further, in the process illustrated in FIG. 12, the degradation
determination part 106A generates the information indicating the
degradation states of the third and fourth solders based on the
measurement results of the third temperature sensor and the fourth
temperature sensor 45 obtained over a whole discharge period of the
smoothing capacitor 20; however, this is not indispensable. For example,
the degradation determination part 106A may generates the information
indicating the degradation states of the third and fourth solders based
on the measurement results of the third temperature sensor 44 and the
fourth temperature sensor 45 obtained over a part of the whole discharge
period of the smoothing capacitor 20 or at a predetermined timing during
the discharge period.

[0096] The present invention is disclosed with reference to the preferred
embodiments. However, it should be understood that the present invention
is not limited to the above-described embodiments, and variations and
modifications may be made without departing from the scope of the present
invention.

[0097] For example, the motor drive circuit 2 illustrated in FIG. 2 does
not include a heat radiating resistor; however, the heat radiating
resistor may be provided in parallel with the smoothing capacitor 20. In
the case where the heat radiating resistor is provided, the current
flowing through the third switching element 15 and the fourth switching
element 16 during the discharge period of the smoothing capacitor 20 may
become smaller; however, the effects described above can be still
obtained.

[0098] Further, the embodiments described above are related to the motor
drive circuit 2 used for the hybrid vehicle or the electric vehicle;
however, the embodiments described above can be applied to a motor drive
circuit used for a power steering apparatus.

[0099] Further, in the embodiments described above, the information
indicating the degradation states by utilizing the timing of starting up
or stopping the system related to the motor drive circuit 2; however, if
similar charge or discharge is performed at other timings, the
information indicating the degradation states may be generated at such
timings.

[0100] Further, according to the embodiments described above, a
configuration in which only one side of the chip of the semiconductor
element as illustrated in FIG. 2 is to be cooled is assumed; however,
such a configuration in which both sides of the chip are to be cooled is
also applicable. Such a configuration in which both sides of the chip are
to be cooled may be such as disclosed in Japanese Laid-open Patent
Publication No. 2012-235081, for example. For example, the chip of the
semiconductor element (the chip of the free wheeling diode 11 in the
example illustrated in FIG. 2, for example) is bonded to substrates
(copper plates, for example) on the upper and lower sides via solders. In
this case, the information indicating the degradation state of the solder
can be generated similarly by regarding the solders on the upper and
lower sides of the chip of the free wheeling diode 11 as a group (through
it is not possible to identify which one is indicated by the
information).

[0101] The present application is based on and claims benefit of priority
of Japanese Priority Application No. 2014-237004, filed on Nov. 21, 2014,
the entire contents of which are hereby incorporated by reference.